Aerosol containers are widely used to package a variety of fluid materials, both liquid and powdered particulate products. Typically, the product and a propellant are confined within the container, at above atmospheric pressure, and the product is released from the container by manually opening a dispensing valve to cause the pressure within the container to deliver the product through the valve and connecting conduits to a discharge orifice.
The dispensing valve, crimped to a mounting cup having a sealing gasket, is normally mounted in a top opening of the container, which opening is defined by a component commonly referred to as the "bead" of the container opening. The mounting cup includes a central pedestal portion for holding the dispensing valve, a profile portion extending outward from the pedestal portion, which profile portion merges into an upwardly extending body portion, the body portion emerging into a hemispherically-shaped channel portion terminating in a skirt portion, which channel portion is configured to receive the bead portion of the container opening. The sealing gasket normally is disposed within the channel portion and in many gasket configurations extends downward along a part of the body portion. After the sealing gasket is disposed onto the mounting cup, the cup is positioned onto the container and the cup is clinched to the container. The clinching operation is well-known to those skilled in the aerosol container art.
The aerosol dispensing valve generally comprises a hollow valve stem having an integral wider base portion, generally referred to as the valve stem body, positioned intermediate between the valve stem and valve stem body is a valve stem groove. A valve housing surrounds the valve stem body, and is crimped and held within the pedestal portion of the mounting cup. A spring is disposed between the bottom of the valve housing and the underside of the valve stem body, and, in many instances, a hollow tube (dip tube) extends from the outside base of the valve housing to the bottom of an associated aerosol container.
The valve stem groove has one or more opening(s) or orifice(s) extending through the valve stem groove wall. An annular valve sealing gasket with a central opening for receiving the valve stem is positioned in the annular valve stem groove, with the orifice(s) within the groove being positioned above the lower surface of the valve gasket when the valve is in the closed position. When the valve is opened by depressing or tilting the valve stem, the valve stem moves axially downwardly or tilts from its upright position to cause the orifice(s) in the annular valve stem groove to move out of registry or sealing relation with the gasket. Product in the aerosol container then, under the influence of the pressure generated by the propellant, passes upwardly through the dip tube into the valve housing, then through the orifice(s) in the annular valve stem groove into the hollow valve stem, and outwardly through an outlet nozzle in an actuator button, cup or spout mounted atop the valve stem.
In an aerosol valve, an effective seal between the valve stem groove and the annular gasket surrounding the groove is critical. Additionally, in an aerosol valve, a further critical seal is the seal between the same annular gasket sealing against the valve stem and the underside of the top portion of the pedestal of the mounting cup and annular upper terminus of the valve housing.
Heretofore, while meeting with significant commercial success, annular gaskets for sealing against the valve stem have comprised a rubber ring having a central opening and a flat, disc-shaped radial portion extending circumferentially from the central opening, which gaskets are die cut from a flat sheet or by cutting from rubber tubing. The aforesaid gaskets of the prior art have been gaskets having a uniform durometer, the most popular compositions being neoprene and buna nitrile rubber having 72 and 55 durometer (Shore A). While acknowledging the success of the prior art valve stem gaskets, there are still a significant number of rejected valves due to a defective sealing between the valve stem gasket and the dual sealing surfaces of said gasket, namely, the seal between the inner portion, including the surface defining the central opening in the gasket, and the valve stem groove and the top and bottom outer portion of the gasket against the underside of the top surface of the pedestal portion of the mounting cup and terminal upper wall portion of the valve housing, respectively.
It is now recognized that the nature of a single durometer gasket contributes to the leaking problem. With a single durometer gasket, there is a compromise in the selection of the single durometer gasket to satisfy the different needs of durometer hardness at the two areas of sealing discussed above, the consequence being that the gasket durometer which would yield the maximum sealing properties at each area is not utilized.